Double-grid thermionic tube



Sit. 25, 1928.

M. VONARDENNE DOUBLE GRID THERMIONIC TUBE Filed Dec. 17, 1926 INVENTQRMANFRED VON ARDENNE BY 8% gw/W ATTORNEY Patented Sept. 25, 1928.

uNiTsD- STATES PATENT OFFICE.

mmrmi) voN ABDENNE, or BERLIN, GERMANY, ASSIGNOR To name oonrommron orAMERICA, A. oonronarron or DELAWARE.

DOUBLE-earn THERMIONIC TUBE.

Application filed December 17, 1926, Serial No. 155,544, and in GermanyDecember 1, 1925.

It is known that tubes equipped with two (and, if desired, more grids)can be used in what is known as the space-charge and the protective gridConnection.

It is also known, that, according to the particular use ofthe tube,either. the one or the other kind of connection offers greateradvantage. Examining the conditions for most favorable amplification ofhigh-frequency alternating current,on the one hand, and low-frequencyalternating current, on the other hand, it is found that one and thesame tube is able to give optimum conditions for both services only bythe adoption of a special form of construction. The two-grid tubesheretofore used either inspace-charge or protective grid connection, sofar as their working characteristics are concerned especially theinverse amplification factor, are nothing but a matter of chance, sothat, for instance, while they may be particularly adva'ntageous foraudio-frequency amplificationin the so-called protective gridconnection, they are unable to give at the same time optimum conditionsfor radio frequency amplification in the space-charge connection.

Now, the special type of tube hereinafter to be described is so designedthat it happens to give best results for low frequency amplification inthe protective grid arrangement,

- while offering most advantages for radio frequency amplification'inthe space-charge connection. Optimum inverse amplification factor(Durchgriif) to be sure, is not a constant magnitude, although testshave shown that inside the customary broadcast wave range,

- i. e., between 200 and 800 meters approximately, an inverseamplification factor of 10% proves best. But an especially favorableaudio-frequency amplification is obtained with the same tube inprotective grid connection, with an inverse amplification factor of 1%.The construction of the tube will.

be described hereinafter in more detail.

As will be seen-: from what precedes, the most particularfeature of, theconstructlon of the present tube-resides in that the same exhibits aninverse amplification factor of 10% when in space-charge connection, andan inverse amplification factor of 1% when arranged in protective gridconnection.

. view of my tube and,

[In the accompanying drawing Fig; 1 shows somewhat diagrammatically -aelevat on .ner grid comprises13fturns, the outer one 18 turns, the wirediameter of both grids being about 0.2 mm. Y

Although the particular dimensions as hereinbefore indicated are merelyindicated to attain the aim of the invention, the basic idea of thelatter is more general. For, as could be shown theoretically, it isalways possible to satisfy simultaneously two conditions with onetwo-grid tube, that is, a definite inverse amplification factor D1 withthe tube arranged in space-charge connection, and another inverseamplification factor D also to be chosen ad lib., with the tube arrangedin protective-grid connection, provided that D does not exceed D. Themeans adapted to insure the desired inverse amplification factors arethemselves well know'n,

and they consist in variable relatix e grid and plate resistances,variable number of'diameters of grid wires, and other secondary and lessimportant factors.

I Now, while in the conventional types of two-grid tubes, the:conditions as to in'verseamplification factor ratios between space--charge and protective-grid connection were a mere matter of chance,these relations according to the present inventiom as above pointed outare to be chosen in such a manner that for the two modes of circuitarrangement and connection the working conditions of the-tubes are sothat there result optimuni dimensions for the various fields ofapplication. It is thus possible to make one and the same tube fordifferent purposes, which" represents a great manufacturing advantageand also a sav ng in tubes, lnd'ecd, only oneloo half the number oftubesis' required since they'ar usable-for a two-fold purpose.

My tubes may be utilized for example, in a circuit of the type shown inFig." 2. Radio ned circuit being :fed

across the radio frequency grid 2-and fila- -ircuit 7, potential vament1 of im roved tube indicated by numeral 5 in-that gure. The radiofrequency output of tube 5 is shunted across an audio frequencytransformer '81by means ,of condenser 9 and is fed into a second tunedcircuit 10, which in turn feeds a detector circuit 11. By means of audiofrequency transformer 12, audio frequency variations and potentials areimpressed across the grid '3 and filament 1 of my tube 5. The resultingamplified audio frequency current variations appearing in the platecircuit of tube 5 arev fed'by means of transformer 8 into a suitablesound producing device 13. In this manner myimproved tube is used bothfor radio frequency amplification and for low frequency amplification.

, I claim as my invention:

A thermionic tube comprising a straight filament substantially2-centimeters long, a

pair of concentric coiled grids about the filamillimeters and havingsubstantially 18- turns, the inner grid being adapted for caus 111g highfrequency variations in the electron stream of the tube, and the outergrid being adapted for causing low frequency varia tions in the electronstream of the tube.

YMANFRED vON ARDENNE.

